Purifying spun cellulose products



Patented Oct. 31, 1933 UNITED STATES PATENT OFFICE N 0 Drawing.

Application September 30, 1930 Serial No. 485,558

2 Claims.

This invention relates to the purification of spun cellulose products and more particularly to a process adapted for desulfurizing spun viscose products and denitrating spun nitro-cellulose products. While the invention is primarily directed to purifying artificial silk filaments it is also adapted for purifying other similar products such as artificial wool, artificial horse hair and the like.

As is well known, spun products of viscose and nitro-cellulose contain objectionable constituents which must be'removed following the spinning of said products. For example, viscose must be desulfurized and nitro-cellulose must be denitrated in order to render the products suitable for commercial use. Numerous processes of desulfurizing spun viscose products and of denitrating spun nitro-cellulose products have been devised and such processes are employed with varying degrees of success. The present invention is concerned with providing a process of desuliurizing spun viscose products and of denitrating spun nitro-cellulose products which is superior to processes commonly employed.

In several of the commercial processes of desulfurizing and denitrating commonly employed, an aqueous bath of ammonium sulfide is employed as the purifying agent. However, such treating material is disadvantageous under many conditions of operation due to the inability of the bath to purify the cellulose products to the desired degr e. In the case of denitrating nitrocellulose filaments with a bath of ammonium sulfide, elemental sulfur is commonly set iree as a result of a secondary reaction and is deposited on the finished filament. The secondary reaction referred to takes place between a portion of the ammonium sulfide in the bath and ammonium nitrite formed when the nitro groups are removed from the nitro-cellulose.

I have discovered that the above referred to disadvantages of employing a bath of ammonium sulfide for denitrating and desulfurizing can be eirectively overcome by introducing into the ammonium sulfide bath sufiicient ammonia or ammonium hydroxide to keep the bath alkaline during the treatment. Practical tests have demonstrated that such a bath containing ammonium sulfide and ammonium hydroxide will take up and hold large amounts of sulfur in the desulfurizing of viscose products and will efiectively serve as a denitrating bath without the liberation of elemental sulfur due to the reaction referred to above. Apparently the presence of the ammonium hydroxide in the bath depresses the secondary reaction mentioned thereby preventing the dropping out of elemental sulfur. This is evidenced in practice by the fact that substantial amounts of ammonium nitrite are present in the treating bath after the treatment has proceeded -for a period.

In the actual practice of the invention, an ammonium sulfide desulfurizing or denitrating bath is made up in the conventional manner and sufficient ammonium hydroxide or ammonia is introduced into the bath to keep it alkaline as set forth above. Ordinarily, a small amount of ammonium hydroxide is efiective for this purpose. I have found that at least 1 per cent. of the bath should consist of ammonium hydroxide and that there is no advantage in increasing this amount over several per cent. except in an unusual case. The amount of ammonium hydroxide may be increased materially without injury to the process but this is disadvantageous from the point of view of economy.

For the sake of a specific example, I have found that an efiective denitrating bath may be made up by employing an aqueous solution of approximately 4 per cent. of ammonium sulfide and 1 per cent. of ammonium hydroxide. As stated above, the exact amounts may be widely varied according to the material treated. The variations will be apparent to those skilled in the art. An effective desulfurizing bath may be made up by employing an aqueous solution of approximately 2 per cent. of ammonium sulfide and at least 1 per cent. of ammonium hydroxide. I-Iere, also, the proportions of ingredients may be varied considerably as will be apparent to those skilled in the art.

The actual manner of subjecting a spun cellulose product to the action of a bath of the character set forth above forms no part of the invention per se. Any conventional manner of treatment may be employed.

While I have described in detail the preferred practice of my process it is to be understood that the details of procedure may be variously modified without departing from the spirit of the invention or the scope of the subjoined claims.

I claim:

1. The herein described process of denitrating spun nitro-cellulose products which comprises subjecting such products to the action of a denitrating agent comprising ammonium sulfide in the presence of ammonium hydroxide.

2. The herein described process of denitrating spun nitro-cellulose products which comprises treating such products in an aqueous bath containing approximately four per cent. of ammonium sulfide and at least one per cent. of ammonium hydroxide.

HARRY P. BASSET'I. 

